CVE-2026-21909

/// Technical description

A Missing Release of Memory after Effective Lifetime vulnerability in the routing protocol daemon (rpd) Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated attacker controlling an adjacent IS-IS neighbor to send a specific update packet causing a memory leak. Continued receipt and processing of these packets will exhaust all available memory, crashing rpd and creating a Denial of Service (DoS) condition.

Memory usage can be monitored through the use of the 'show task memory detail' command. For example:

user@junos> show task memory detail | match ted-infra

  TED-INFRA-COOKIE           25   1072     28   1184     229

user@junos>

show task memory detail | match ted-infra

  TED-INFRA-COOKIE           31   1360     34   1472     307

This issue affects:

Junos OS: 

* from 23.2 before 23.2R2, 

* from 23.4 before 23.4R1-S2, 23.4R2, 

* from 24.1 before 24.1R2; 

Junos OS Evolved: 

* from 23.2 before 23.2R2-EVO, 

* from 23.4 bef

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References